What does "regulus" mean?

Regulus: (Chem. & Metal.) The button, globule, or mass of metal, in a more or less impure state, which forms in the bottom of the crucible in smelting and reduction of ores. Note: The name was introduced by the alchemists, and applied by them in the first instance to antimony. Ilittle king; and from the facility with which antimony alloyed with gold, these empirical philosophers had great hopes that this metal, antimony, would lead them to the discovery of the philosopher's stone. Ure.